核心代码：

//datatable dt 存储表（name，sex），自己写

TreeNode node1，node2;

for (int i = 0; i < dt.Rows.Count; i++)
{

   if(dt.Rows[i][1].ToString().Trim()=='男')

     {  

        node1.Nodes.Add(dt.Rows[i][0].ToString().Trim());

     }

else  if(dt.Rows[i][1].ToString().Trim()=='女')

    {

          node2.Nodes.Add(dt.Rows[i][0].ToString().Trim());

    }
}

treeView1.Nodes.Add(node1);

treeView1.Nodes.Add(node2);

OK，完毕。

        private void Form1_Load(object sender, EventArgs e)
        {
            TreeNode menNode = new TreeNode();
            menNode.Text = "男";
            TreeNode femaleNode = new TreeNode();
            femaleNode.Text = "女";
            treeView1.Nodes.Add(menNode);
            treeView1.Nodes.Add(femaleNode);
            DataTable dt = GetUser();
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                DataRow dr = dt.Rows[i];
                TreeNode childNode = new TreeNode();
                if (dr[1].ToString()=="男")
                {
                    childNode.Text = dr[0].ToString();
                    menNode.Nodes.Add(childNode);
                }
                else if(dr[1].ToString()=="女")
                {
                 
                    childNode.Text = dr[0].ToString();
                    femaleNode.Nodes.Add(childNode);
                }
            }
            //展开
            menNode.ExpandAll();
            femaleNode.ExpandAll();
        }

 /// <summary>
        /// 模拟从数据库 读取的数据 返回DataTable
        /// </summary>
        /// <returns></returns>
        private DataTable GetUser()
        {
            DataTable dt = new DataTable();
            DataColumn columnName = new DataColumn("Name", typeof(string));
            DataColumn columnSex = new DataColumn("Sex", typeof(string));
            dt.Columns.Add(columnName);
            dt.Columns.Add(columnSex);
            DataRow row = dt.NewRow();
            row[0] = "张三";
            row[1] = "男";
            dt.Rows.Add(row);
            DataRow row2 = dt.NewRow();
            row2[0] = "李四";
            row2[1] = "男";
            dt.Rows.Add(row2);
            DataRow row3 = dt.NewRow();
            row3[0] = "丽力";
            row3[1] = "女";
            dt.Rows.Add(row3);
            return dt;
        }

测试结果

public void tvBind()
        {
            DataSet ds_BuMen = getDataSet("BuMen");
            DataSet ds_BLGB = getDataSet("BLGB");
            foreach (DataRow dr in ds_BuMen.Tables[0].Rows)
            {
                //部门表绑定，作为一级层次
                TreeNode tn_origine = new TreeNode();
                tn_origine.Text = dr["BMMC"].ToString();
                this.tvShow.Nodes.Add(tn_origine);
                //病人表绑定
                DataRow[] dr_arr = ds_BLGB.Tables[0].Select("BRBM=" + int.Parse(dr["id"].ToString()));
                if (dr_arr.Length > 0)
                {  
                    foreach (DataRow dr_sub in dr_arr)
                    {
                        TreeNode tn_sub = new TreeNode();
                        tn_sub.Text = dr_sub["BRXM"].ToString();
                        tn_origine.Nodes.Add(tn_sub);
                    }                   
                }
            }
        }

Datatable 中的Filters、Comput是两个不错的东东。